The Ebola virus has been responsible for at least 10 outbreaks with a 50-90% human case fatality, has no available vaccines or treatments, and has an alarming potential as an instrument of bioterrorism. Certain proteins of the Ebola virus play a role in its extraordinary pathogenesis and lethality. The specific aims of this application are to crystallize these proteins (VP35, sGP, and GP) and also the human antibody KZ52, for structural analysis. (1) The VP35 protein blocks interferon activation of immunomodulatory genes and may play a significant role in Ebola virus suppression of the host immune system. Structural analysis of the VP35 protein may provide critical clues for the design of anti-viral compounds and attenuated viral strains. (2 and 3) The sGP and GP proteins share 295 amino acids of N-terminal sequence, but have differing C terminal sequences. The differing C termini result in unique patterns of disulfide bonding, quaternary structure, and roles in pathogenesis. sGP is secreted in large quantities while GP remains on the viral surface to function in viral attachment, fusion, and tropism. Comparative structural analysis of GP and sGP should illustrate how two structures may arise from the same sequence, and provide templates critical to the design of vaccines to elicit antibodies that target the virus and not secreted decoy proteins. (4) The human antibody KZ52, cloned from the bone marrow of a survivor of the 1995 Kikwit, Zaire outbreak, is capable of potently neutralizing the Ebola virus. A structure of KZ52 will contribute to an understanding of how an effective humoral immune response against the Ebola virus might be generated, and will assist in the design of immunogens to elicit potent KZ52-like antibodies. Structural analysis of VP35, sGP, GP, and KZ52 would provide information seminal not just to the design of vaccines and inhibitors against the Ebola virus as it exists naturally, but also to the development of structural templates that would permit us to anticipate and rapidly respond to man-made versions of the virus and viral proteins.